Refrigeration cycle apparatus

ABSTRACT

A refrigeration cycle apparatus includes a compressor, a radiator, an expander, an evaporator, a bypass circuit, and an injection circuit. The bypass circuit has a flow rate control valve and a gas-liquid separator. One end of the bypass circuit is connected to an intake conduit of the expander and the other end thereof is connected to a discharge conduit of the expander so that a portion of refrigerant passed through the radiator bypasses the expander and is guided to the flow rate control valve and that the liquid refrigerant separated by the gas-liquid separator returns to the discharge conduit of the expander. One end of the injection circuit is connected to a gas outlet portion of the gas-liquid separator and the other end thereof is connected to an intermediate pressure portion of the compressor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a refrigeration cycle apparatus appliedto hot water heaters, air-conditioners, and the like, and moreparticularly to a configuration and a control method therefor thatachieve high efficiency by mixing a refrigerant that flows through abypass circuit with a refrigerant that is in the process of compression.

2. Description of Related Art

A known refrigeration cycle apparatus uses a fluid machine in which botha positive displacement compressor and a positive displacement expanderare coupled uniaxially so that the energy of expansion of therefrigerant recovered by the expander can be used as auxiliary drivingpower for the compressor. In this kind of refrigeration cycle apparatus,the compressor and the expander constantly rotate at the same frequency.Unless some special mechanism is provided, the intake capacity of thecompressor and the intake capacity of the expander are also constant.Therefore, theoretically, the ratio between the density pc of thecompressor's intake refrigerant and the density pe of the expander'sintake refrigerant is constant at all times. When this constraint ofconstant density ratio exists, the refrigeration cycle apparatus is notpermitted to operate outside that constraint. Thus, although such anapparatus originally is intended to achieve high cycle efficiency by thepower recovery with the use of the expander, it does not necessarilyachieve a high efficiency operation.

FIG. 12 illustrates a system that employs a bypass circuit for resolvingsuch an issue. This system is provided with a control valve 12 forvariably adjusting the passage area of the bypass circuit 11. Byadjusting the opening of the control valve 12 to regulate therefrigerant flow rate passing through the expander 4 variably, the massflow rate of the refrigerant that passes through the compressor 3 andthe mass flow rate of the refrigerant that passes through the expander 4may be made different from each other. In other words, the conventionalconstraint of constant density ratio on the cycle operation iseliminated (see, for example, JP 2001-116371A (FIG. 1)).

JP 2003-121018A discloses a refrigeration cycle apparatus including acompressor and an expander that are coupled directly by a single shaft.The refrigeration cycle apparatus has an expansion valve arranged inseries with the expander, and a bypass valve for bypassing the expander.A gas-liquid separator is provided between the expander and theexpansion valve so that the gas refrigerant separated from the liquidrefrigerant by the gas-liquid separator is introduced to an intermediatepressure portion of the compressor.

SUMMARY OF THE INVENTION

However, a problem has been that the refrigerant flowing through thecircuit that bypasses the expander does not contribute to improvementsin system efficiency at all. This applies to both of the foregoingpublications.

In view of this, it is an object of the present invention to provide arefrigeration cycle apparatus provided with a compressor, a radiator, anexpander, and an evaporator, connected successively in series, that canincrease the refrigerant flow rate through the radiator and at the sametime avoid the constraint of constant density ratio.

Accordingly, the present invention provides refrigeration cycleapparatus including:

a compressor for compressing a refrigerant;

a radiator for cooling the refrigerant compressed by the compressor;

an expander for expanding the refrigerant cooled by the radiator andrecovering mechanical power from the refrigerant under expansion;

an evaporator for heating the refrigerant expanded by the expander andsupplying the refrigerant to the compressor;

a bypass circuit including a flow rate control valve and a gas-liquidseparator that is provided downstream from the flow rate control valveand that is for separating the refrigerant passed through the flow ratecontrol valve into a gas refrigerant and a liquid refrigerant, one endof the bypass circuit being connected to an intake conduit of theexpander and the other end of the bypass circuit being connected to adischarge conduit of the expander so that a portion of the refrigerantpassed through the radiator bypasses the expander and is guided to theflow rate control valve and that the liquid refrigerant separated by thegas-liquid separator returns to the discharge conduit of the expander;and

an injection circuit, one end of which being connected to a gas outletportion of the gas-liquid separator and the other end of which beingconnected to an intermediate pressure portion of the compressor.

According to the present invention as described above, by allowing aportion of the refrigerant flowing out of the radiator to flow throughthe bypass circuit, the constraint of constant density ratio can beavoided. Moreover, since the liquid refrigerant and the gas refrigerantare separated by the gas-liquid separator provided in the bypass circuitand the gas refrigerant is injected into the intermediate pressureportion of the compressor, the refrigerant flow rate through theradiator can be increased. The specific enthalpy of the liquidrefrigerant that flows out of the gas-liquid separator and returns tothe discharge conduit of the expander is smaller than the specificenthalpy of the refrigerant (gas-liquid two-phase refrigerant) that hasbeen expanded by the expander. Therefore, the specific enthalpy of therefrigerant at the inlet of the evaporator lowers and the enthalpydifference between the inlet and the outlet of the evaporator increases,leading to an improvement in the refrigerating capacity. Furthermore,the injection circuit enables the gas refrigerant flowing out of thegas-liquid separator to be mixed with the refrigerant that is in thecompression process, preventing liquid compression from occurring in thecompressor and thus ensuring a high degree of reliability of thecompressor.

In another aspect, the present invention provides a refrigeration cycleapparatus including:

a compressor for compressing a refrigerant;

a radiator for cooling the refrigerant compressed by the compressor;

an expander for expanding the refrigerant cooled by the radiator andrecovering mechanical power from the refrigerant under expansion;

an evaporator for heating the refrigerant expanded by the expander andsupplying the refrigerant to the compressor;

a bypass circuit including a flow rate control valve, one end of thebypass circuit being connected to an intake conduit of the expander andthe other end of the bypass circuit being connected to an intermediatepressure portion of the compressor so that a portion of the refrigerantpassed through the radiator bypasses the expander and is guided to theflow rate control valve;

an intake temperature sensor for detecting the refrigerant after flowingout of the evaporator but before being taken into the compressor; and

a controller for controlling an opening of the flow rate control valveaccording to a detection result detected by the intake temperaturesensor.

According to the present invention as described above, by allowing therefrigerant to flow through the bypass circuit, the refrigerant flowrate through the radiator can be increased while the constraint ofconstant density ratio is avoided. Therefore, the overall performance ofthe refrigeration cycle apparatus can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration diagram illustrating a refrigeration cycleapparatus according to a first embodiment of the present invention;

FIG. 2 is a vertical cross-sectional view illustrating one example of afluid machine including a compressor and an expander;

FIG. 3 is a view illustrating one example of injection ports provided inthe compressor;

FIG. 4 is a Mollier diagram illustrating the refrigeration cycleaccording to the first embodiment of the present invention;

FIG. 5 is a control flow diagram of the refrigeration cycle apparatusaccording to the first embodiment of the present invention;

FIG. 6 is a configuration diagram illustrating a refrigeration cycleapparatus according to a second embodiment of the present invention;

FIG. 7 is a configuration diagram illustrating a refrigeration cycleapparatus according to a third embodiment of the present invention;

FIG. 8 is a configuration diagram illustrating a refrigeration cycleapparatus according to a fourth embodiment of the present invention;

FIG. 9 is a configuration diagram illustrating a refrigeration cycleapparatus according to a fifth embodiment of the present invention;

FIG. 10 is a Mollier diagram illustrating the refrigeration cycleaccording to the fifth embodiment of the present invention;

FIG. 11 is a control flow diagram of the refrigeration cycle apparatusaccording to the fifth embodiment of the present invention; and

FIG. 12 is a configuration diagram illustrating a conventionalrefrigeration cycle apparatus.

DETAILED DESCRIPTION OF THE INVENTION

Hereinbelow, embodiments of the refrigeration cycle apparatus accordingto the present invention will be described in detail with reference tothe drawings.

FIRST EMBODIMENT

FIG. 1 is a configuration diagram illustrating a refrigeration cycleapparatus according to a first embodiment of the present invention. Arefrigeration cycle apparatus 100A of the present embodiment isfurnished with a compressor 101 for compressing a refrigerant such ashydrofluorocarbon or carbon dioxide, a radiator 102 for cooling therefrigerant compressed by the compressor 101, an expander 103 fordecompressing and expanding the refrigerant cooled by the radiator 102and recovering mechanical power from the refrigerant under expansion, anevaporator 104 for heating the refrigerant decompressed by the expander103, and a plurality of main pipes 116 (main conduits) for connectingthe compressor 101, the radiator 102, the expander 103, and theevaporator 104 in that order. The compressor 101, the radiator 102, theexpander 103, the evaporator 104, and the main pipes 116 constitute amain circuit 117 through which the refrigerant circulates.

In the first embodiment, the compressor 101 and the expander 103 arecoupled uniaxially to a motor 6 for driving the compressor 101. FIG. 2is a vertical cross-sectional view illustrating one example of fluidmachine including the compressor 101 and the expander 103 of this kind,and according to the present embodiment, the refrigeration cycleapparatus 100A includes such a fluid machine 200. As illustrated in FIG.2, mechanical power obtained by the expander 103 is supplied to a shaft7 and is utilized as auxiliary driving power for the compressor 101,which contributes to reducing the power consumption of the motor 6.Since the expander 103 and the compressor 101 revolve at the samefrequency at all times, the refrigeration cycle apparatus including thefluid machine 200 is constrained by the constraint of constant densityratio.

As a means to avoid the constraint of constant density ratio, therefrigeration cycle apparatus 100A is, as illustrated in FIG. 1, furtherfurnished with a bypass circuit 113, one end of which is connected toone of the main pipes 116 that is between the radiator 102 and theexpander 103 and the other end of which is connected to another one ofthe main pipes 116 that is between the expander 103 and the evaporator104, so that a portion of the refrigerant that has passed through theradiator 102 bypasses the expander 103. The former of the main pipes 116is an intake conduit of the expander 103 and is also a discharge conduitof the radiator 102. The latter of the main pipes 116 is a dischargeconduit of the expander 103 and is also an intake conduit of theevaporator 104.

The bypass circuit 113 includes a first flow rate control valve 105, agas-liquid separator 110 provided downstream from the first flow ratecontrol valve 105, and a plurality of bypass pipes 115. By allowing aportion of the refrigerant that has passed through the radiator 102 toflow through the bypass circuit 113, the ratio between the density ofthe refrigerant at the inlet of the compressor 101 and the density ofthe refrigerant at the inlet of the expander 103 can be varied.

The refrigerant that bypasses the expander 103 is introduced to thefirst flow rate control valve 105. The gas-liquid separator 110 has thefunction of separating the refrigerant that has passed through the firstflow rate control valve 105 into a gas refrigerant and a liquidrefrigerant, and it has a liquid outlet portion and a gas outletportion. A bypass pipe 115 is connected to the liquid outlet portion sothat the gas-liquid two-phase refrigerant that has changed from theliquid refrigerant into the gas-liquid two-phase refrigerant can bereturned to one of the main pipes 116 that is between the expander 103and the evaporator 104.

The refrigeration cycle apparatus 100A further includes an injectioncircuit 109, one end of which is connected to the gas outlet portion ofthe gas-liquid separator 110 and the other end of which is connected toan intermediate pressure portion of the compressor 101 (an intermediatepressure portion of the main circuit 117). The injection circuit 109includes a second flow rate control valve 108 and a plurality ofinjection pipes 119. A portion or all of the gas refrigerant that hasbeen separated from the liquid refrigerant by the gas-liquid separator110 is injected into the intermediate pressure portion of the compressor101 through the injection circuit 109.

As illustrated in FIG. 2, the intermediate pressure portion of thecompressor 101 can be a portion of the interior of the compressor 101that faces the refrigerant flow channel, that is, a portion thereof thatfaces a compression chamber 28. The compressor 101 is a scroll-typecompressor in which the compression chamber 28 is formed between astationary scroll 21 and an orbiting scroll 22, and an injection port120 provided in the stationary scroll 21 serves as the intermediatepressure portion. One of the injection pipes 119 is connected to theinjection port 120. The injection port 120 is located between an intakeport 21 a and an outlet port 21 b in the refrigerant flow channel withinthe compressor 101. The gas refrigerant that has flowed out of the gasoutlet portion of the gas-liquid separator 110 passes through theinjection circuit 109, is injected into the compression chamber 28through the injection port 120, and is mixed with the refrigerant thatis being compressed.

An injection port 120 may be provided at one location in the stationaryscroll 21, or, as illustrated in FIG. 3, a plurality of injection ports120, 120 may be provided at a plurality of locations in the stationaryscroll 21. The type of the compressor is not limited to the scroll type,and may be other types of positive displacement compressors such as arotary type compressor. Likewise, the type of the expander is notlimited either, although FIG. 2 shows a two-stage rotary compressor asthe expander 103.

It should be noted that in the present specification the term“intermediate pressure” is intended to mean a pressure that is between ahigh pressure and a low pressure in the refrigeration cycle, in otherwords, a pressure between the pressure of the refrigerant flowing intothe radiator 102 and the pressure of the refrigerant flowing out of theevaporator 104.

Referring back to FIG. 1, the description will proceed further. Thebypass circuit 113 further may include a throttling device 114 provideddownstream from the gas-liquid separator 110. The throttling device 114may be a common expansion valve. Such a throttling device 114 is capableof changing the liquid refrigerant flowing out of the gas-liquidseparator 110 into a gas-liquid two-phase refrigerant. This allows thegas-liquid two-phase refrigerant to be returned to the main pipe 116that is between the expander 103 and the evaporator 104, which isadvantageous in maintaining a desired operating condition. However, ifthe amount of the liquid refrigerant is small, it is possible to sendthe liquid refrigerant to the main pipe 116 without expanding it by thethrottling device 114. It should be noted that the first flow ratecontrol valve 105, the second flow rate control valve 108, and thethrottling device 114 have a common function, so the same kind ofexpansion valves may be used for them.

In addition, it is recommended that two temperature sensors 111 and 112be provided as a means for detecting the temperature of the refrigerantthat circulates in the main circuit 117. One of the temperature sensors111 is an intake temperature sensor that detects the temperature of therefrigerant after flowing out of the evaporator 104 but before beingtaken into the compressor 101, and it detects what is called a superheattemperature. The other one of the temperature sensors 112 is an outlettemperature sensor that detects the temperature of the refrigerant afterbeing discharged from the compressor 101 but before flowing into theradiator 102. Furthermore, a controller 107 is provided, which controlsthe openings of the first flow rate control valve 105 and the throttlingdevice 114 of the bypass circuit 113 as well as the opening of thesecond flow rate control valve 108 of the injection circuit 109. Signalsthat can identify the temperatures of the refrigerant are input from thetwo temperature sensors 111 and 112 to the controller 107. Thecontroller 107 controls the openings of the first flow rate controlvalve 105, the throttling device 114, and the second flow rate controlvalve 108 according to the signals from the temperature sensors 111 and112. This makes it possible to optimize the efficiency of therefrigeration cycle apparatus 100A.

The operations and effects of the refrigeration cycle apparatus 100Awill be described with reference to the Mollier diagram of FIG. 4.

In the Mollier diagram of FIG. 4, the change of the refrigerantcirculating in the main circuit 117 is represented as A→B→C→D→E→F→A. Therefrigerant flowing through the bypass circuit 113 is branched at pointE, which corresponds to the portion of the main circuit 117 that isbetween the radiator 102 and the expander 103, is then decompressed topoint G by the first flow rate control valve 105, and is thereafterseparated into a gas refrigerant and a liquid refrigerant by thegas-liquid separator 110. The liquid refrigerant, which is in the stateof point H on the saturated liquid curve, is decompressed to point I bythe throttling device 114, and is then merged with the refrigerant beingat point F, which is discharged from the expander 103. Accordingly, thespecific enthalpy of the refrigerant that has been discharged from theexpander 103 and merged with the liquid refrigerant from the bypasscircuit 113 is represented by point J. On the other hand, the gasrefrigerant separated from the liquid refrigerant by the gas-liquidseparator 110 flows into the compressor 101 and merges with therefrigerant at point B, which is the refrigerant under compression. Thespecific enthalpy of the refrigerant that has undergone the merge withthe refrigerant being compressed by the compressor 101 and the gasrefrigerant injected from the injection circuit 109 is represented bypoint C.

The refrigerant flow rate flowing through the radiator 102 is the sum ofthe refrigerant flow rate Ge flowing through the evaporator 104 and therefrigerant flow rate Gi flowing through the bypass circuit 106, andthus is represented as (Ge+Gi); therefore, the amount of heat exchangedby the radiator increases. In this way, it is possible to improve theperformance of the refrigeration cycle apparatus 100A while avoiding theconstraint of constant density ratio.

When the refrigerant flow rate flowing through the bypass circuit 113 isincreased, the refrigeration cycle will be balanced so that the intakedensity of the compressor 101 increases. Accordingly, when the intakesuperheat of the compressor 101 needs to be reduced, the opening of thefirst flow rate control valve 105 provided in the bypass circuit 113should be increased.

In addition, by increasing the opening of the second flow rate controlvalve 108 provided in the injection circuit 109 so as to increase therefrigerant flow rate flowing through the injection circuit 109, thespecific enthalpy at point C becomes smaller, and thereby, therefrigerant discharge temperature (point D) of the compressor 101 can becontrolled to be lower.

Thus, when the refrigerant flow rate flowing through the injectioncircuit 109 is increased, the refrigeration cycle will be balanced sothat the refrigerant discharge temperature of the compressor 101decreases. Conversely, when it is desired to elevate the refrigerantdischarge temperature of the compressor 101, the opening of the secondflow rate control valve 108 provided in the injection circuit 109 shouldbe decreased.

The control procedure for the first flow rate control valve 105 and thesecond flow rate control valve 108 executed by the controller 107 willbe described with reference to the flowchart of FIG. 5. Upon startingthe operation, it is assessed at step 301 whether or not the differencebetween an actual superheat temperature T1 detected by the intaketemperature sensor 111 and a target superheat TH1 falls within thetolerance range ±t₁ (dead zone). The tolerance t₁ may be set to be about5% of the target superheat TH1.

If it is assessed that the difference (absolute value) between theactual superheat temperature T1 and the target superheat TH1 is greaterthan the tolerance t₁, the process proceeds to step 302, in which it isassessed whether or not the actual superheat temperature T1 is greaterthan the target superheat TH1. If the actual superheat temperature T1 isgreater than the target superheat TH1, the process proceeds to step 303,in which a control process for increasing the opening of the first flowrate control valve 105 is executed. When the opening of the first flowrate control valve 105 is increased, the refrigerant flow rate flowingthrough the bypass circuit 113 increases; therefore, the refrigerationcycle will be balanced so that the superheat temperature T1 decreases.

On the other hand, if it is assessed at step 302 that the actualsuperheat temperature T1 is lower than the target superheat TH1, theprocess proceeds to step 304, in which a control process for decreasingthe opening of the first flow rate control valve 105 is executed.Thereby, the refrigeration cycle will be balanced so that the superheattemperature T1 rises, and therefore, the superheat temperature can becontrolled so as to approach the target value.

Next, it is assessed at step 305 whether or not the difference betweenan actual refrigerant discharge temperature T2 detected by the outlettemperature sensor 112 and a target refrigerant discharge temperatureTH2 falls within the tolerance range ±t₂ (dead zone). The tolerance t₂may be set to be about 5% of the target refrigerant dischargetemperature, for example. If it is assessed that the difference betweenthe actual refrigerant discharge temperature T2 and the targetrefrigerant discharge temperature TH2 falls within the tolerance range±t₂, the control process is terminated.

On the other hand, if it is assessed at step 305 that the differencebetween the actual refrigerant discharge temperature T2 and the targetrefrigerant discharge temperature TH2 (absolute value) is greater thanthe tolerance t₂, the process proceeds to step 306, in which it isassessed whether or not the actual refrigerant discharge temperature T2is greater than the target refrigerant discharge temperature TH2. If theactual refrigerant discharge temperature T2 is greater than the targetrefrigerant discharge temperature TH2, the process proceeds to step 307,in which a control process for increasing the opening of the second flowrate control valve 108 is executed. Increasing the opening of the secondflow rate control valve 108 results in a greater refrigerant flow rateflowing through the injection circuit 109, and therefore, therefrigeration cycle will be balanced so that the refrigerant dischargetemperature T2 decreases. Referring to the Mollier diagram of FIG. 4,the specific enthalpy at point C becomes smaller, and the refrigerantdischarge temperature T2 of the compressor 101 (temperature at point D)decreases.

If it is assessed at step 306 that the actual refrigerant dischargetemperature T2 is lower than the target refrigerant dischargetemperature TH2, the process proceeds to step 308, in which a controlprocess for decreasing the opening of the second flow rate control valve108 is executed. Thereby, the refrigeration cycle will be balanced sothat the refrigerant discharge temperature T2 rises, and therefore, therefrigerant discharge temperature can be controlled so as to approachthe target value. According to the Mollier diagram of FIG. 4, thespecific enthalpy at point C increases, and the refrigerant dischargetemperature T2 of the compressor 101 (temperature at point D) rises. Ifthe opening of the second flow rate control valve 108 is changed, theprocess returns to step 301. By executing the control process depictedin the flowchart of FIG. 5 repeatedly, in other words, by executing thecontrol process periodically as needed, the superheat temperature andthe refrigerant discharge temperature always can be kept at optimalvalues.

As has been described above, adjusting the openings of the first flowrate control valve 105 and the second flow rate control valve 108 tocontrol the superheat temperature and the refrigerant dischargetemperature enables the system performance to be kept optimally highwhile avoiding the constraint of constant density ratio.

The foregoing has described an embodiment in which the openings of thefirst and second flow rate control valves 105 and 108 are adjusted usingthe superheat temperature and the refrigerant discharge temperature ofthe compressor 101. The openings of the first and second flow ratecontrol valves 105 and 108 may be controlled by one or a plurality ofparameters selected from the group consisting of the superheattemperature, the refrigerant discharge temperature of the compressor101, the high pressure of the refrigeration cycle, the evaporatortemperature, and the frequency of the compressor 101, in addition to thecombination of the superheat temperature and the refrigerant dischargetemperature of the compressor 101.

SECOND EMBODIMENT

The first embodiment has described the case in which the injectioncircuit 109 is connected directly to the compressor 101. By contrast,the refrigeration cycle apparatus according to the second embodimentdiffers from the first embodiment in that it has a plurality ofcompressors. It should be noted, however, that the advantageous effectsachieved by the bypass circuit and the injection circuit are commonbetween the second embodiment and the first embodiment.

As illustrated in FIG. 6, a refrigeration cycle apparatus 100B of thesecond embodiment is furnished with a low-pressure-side compressor 101A,and a high-pressure-side compressor 101B connected in series with thelow-pressure-side compressor 101A via one of the main pipes 116.Specifically, a multi-stage compressor including the low-pressure-sidecompressor 101A and the high-pressure-side compressor 101B is employedas the compressor for compressing a refrigerant. In this case, theintermediate pressure portion of the compressors 101A and 101B, to whichthe injection circuit 109 is connected, may be the main pipe 116 that isa joint portion for joining the low-pressure-side compressor 101A andthe high-pressure-side compressor 101B. According to the presentembodiment, the injection circuit 109 and the compressors 101A, 101B canbe connected by connecting the injection pipe 119 and the main pipe 116,so the designing and assembling of the apparatus are made easy. Ofcourse, a connecting component such as a joint may be provided betweenthe injection pipe 119 and the main pipe 116.

The compressor that is coupled uniaxially to the expander 103 may beeither the low-pressure-side compressor 101A or the high-pressure-sidecompressor 101B. The type of each of the compressors 101A and 101B isnot particularly limited, and various types of positive displacementcompressors such as a scroll type, a rotary type, or a reciprocatingtype compressor may be employed suitably. In addition, the type of thecompressor that is not coupled uniaxially to the expander 103 may be acentrifugal compressor.

THIRD EMBODIMENT

FIG. 7 illustrates a configuration diagram of a refrigeration cycleapparatus according to a third embodiment. A refrigeration cycleapparatus 100C shown in FIG. 7 differs from that of the first embodimentin that an injection circuit 109′ further includes an injector 123provided downstream from the second flow rate control valve 108. Inother respects, the present embodiment is similar to the firstembodiment, and in the drawings, the same reference numerals designatethe same components.

The injector 123 in the injection circuit 109′ is capable of switchingbetween an open state that permits passage of the refrigerant (gasrefrigerant) and a closed state that inhibits passage of therefrigerant, and it may be, for example, a solenoid valve controlled bythe controller 107. Thus, the present embodiment makes it possible tocontrol even the timing of injecting the gas refrigerant into theintermediate pressure portion of the compressor 101. For example, bycontrolling the open/close operations of the injector 123 so as tosynchronize the rotation of the compressor 101, the gas refrigerant canbe injected into the compression chamber 28 inside the compressor 101with more appropriate timing. It should be noted that the second flowrate control valve 108 may be omitted and only the injector 123 of thiskind may be provided. The injector 123 may be disposed inside the shellof the compressor 101.

FOURTH EMBODIMENT

FIG. 8 illustrates a configuration diagram of a refrigeration cycleapparatus according to a fourth embodiment. A refrigeration cycleapparatus 100D shown in FIG. 8 additionally has a liquid refrigerantreturn circuit 125 for enabling the expander 103 to take in the liquidrefrigerant that has been separated from the gas refrigerant by thegas-liquid separator 110, in addition to the elements of therefrigeration cycle apparatus of the first embodiment.

The liquid refrigerant return circuit 125 may be constituted by asimilar pipe such as that used for the main pipes 116 and the bypasspipes 115. One end of the liquid refrigerant return circuit 125 isconnected to a portion of the bypass circuit 113 that is between theliquid outlet portion of the gas-liquid separator 110 and the throttlingdevice 114. The other end of the liquid refrigerant return circuit 125is connected to the intake conduit of the expander 103 (corresponding toa portion of the main pipes 116) downstream from the branching locationto the bypass circuit 113. One end of the liquid refrigerant returncircuit 125 may be connected to the liquid outlet portion of thegas-liquid separator 110, and the other end thereof may be connected tothe inlet (or a neighboring part of the inlet) of the expander 103.

By restricting the opening of the throttling device 114, a portion ofthe liquid refrigerant separated from the gas refrigerant by thegas-liquid separator 110 can be supplied to the liquid refrigerantreturn circuit 125. After circulating through the liquid refrigerantreturn circuit 125, the liquid refrigerant is taken into the expander103. Thus, the refrigerant flow rate through the expander 103 can beincreased, and therefore, the amount of power recovery can be increasedand further improvement in the efficiency can be expected. Of course,the constraint of constant density ratio can be avoided because of theworking of the injection circuit 109.

In addition, it is possible to supply the whole amount of the liquidrefrigerant that has been separated from the gas refrigerant by thegas-liquid separator 110 to the liquid refrigerant return circuit 125 byfully closing the throttling device 114. Under certain circumstances,the throttling device 114 and the bypass pipe 115 downstream from thethrottling device 114 may be omitted. Furthermore, the liquidrefrigerant return circuit 125 may include a flow rate control valve(not shown).

FIFTH EMBODIMENT

FIG. 9 illustrates a configuration diagram of a refrigeration cycleapparatus according to a fifth embodiment. A refrigeration cycleapparatus 100E is furnished with a main circuit 117 and a bypass circuit106. The configuration of the main circuit 117 is the same as that ofthe other embodiments, but the configuration of the bypass circuit 106is different from that of the other embodiments.

As illustrated in FIG. 9, the bypass circuit 106 connects the intakeconduit of the expander 103 and the intermediate pressure portion of thecompressor 101 via the first flow rate control valve 105, and it is thecircuit for introducing a portion of the refrigerant that has passedthrough the radiator 102 to the intermediate pressure portion of thecompressor 101. As has been explained previously, the injection port(s)120 (see FIG. 2) of the compressor 101 may be used as the intermediatepressure portion of the compressor 101.

As illustrated in the Mollier diagram of FIG. 10, the change of therefrigerant circulating in the main circuit 117 is represented asA→B→C→D→E→F→A. The refrigerant flowing through the bypass circuit 106 isbranched at point E, which corresponds to the portion of the maincircuit 117 that is between the radiator 102 and the expander 103, isthen decompressed to point G by the first flow rate control valve 105,and thereafter is introduced into the intermediate pressure portion ofthe compressor 101, which is represented as point C. The refrigerantflow rate flowing through the radiator 102 is the sum of the refrigerantflow rate Ge flowing through the evaporator 104 and the refrigerant flowrate Gi flowing through the bypass circuit 106, and thus is representedas (Ge+Gi); therefore, the amount of heat exchanged by the radiatorincreases. In this way, it is possible to improve the performance of therefrigeration cycle apparatus 100E while avoiding the constraint ofconstant density ratio.

Here, the following equations (1) and (2) hold, wherein: the volume flowrate of the refrigerant that passes through the compressor 101 isrepresented as VC; the refrigerant density at the inlet of thecompressor 101 is DC; the volume flow rate of the refrigerant thatpasses through the expander 103 is VE; the refrigerant density at theinlet of the expander 103 is DE; and the mass flow rate ratio of therefrigerant that flows through the bypass circuit 113 with respect tothe total refrigerant is h, whereby the mass flow rate ratio of therefrigerant that flows through the expander 103 can be expressed as(1−h). It should be noted that the mass flow rate ratio of thecompressor 101 is approximated as “1.”VC×DC:VE×DE=1:(1−h)  (1)VE×DE=(1−h)×VC×DC  (2)

According to these relationships, when the refrigerant flow rate flowingthrough the bypass circuit 106 is increased, the refrigeration cyclewill be balanced so that the refrigerant density DC at the inlet of thecompressor 101 increases. Accordingly, when the intake superheat of thecompressor 101 is desired to be reduced, the opening of the first flowrate control valve 105 provided in the bypass circuit 106 should beincreased.

The control procedure for the first flow rate control valve 105 executedby the controller 107 will be described with reference to the flowchartof FIG. 11. Upon starting the operation, it is assessed at step 201whether or not the difference between an actual superheat temperature T1detected by the intake temperature sensor 111 and a target superheat TH1falls within the tolerance range ±t₁ (dead zone). The tolerance ti maybe set to be about 5% of the target superheat TH1. If it is assessedthat the difference between the actual superheat temperature T1 and thetarget superheat TH1 falls within the tolerance range ±t₁, the controlprocess is terminated.

On the other hand, if it is assessed that the difference between theactual superheat temperature T1 and the target superheat TH1 (absolutevalue) is greater than the tolerance t₁, the process proceeds to step202, in which it is assessed whether or not the actual superheattemperature T1 is greater than the target superheat TH1. If the actualsuperheat temperature T1 is greater than the target superheat TH1, theprocess proceeds to step 203, in which a control process for increasingthe opening of the first flow rate control valve 105 is executed.Increasing the opening of the first flow rate control valve 105 resultsin a greater refrigerant flow rate flowing through the bypass circuit106, and therefore, the refrigeration cycle will be balanced so that thesuperheat temperature T1 decreases. If it is assessed at step 202 thatthe actual superheat temperature T1 is lower than the target superheatTH1, the process proceeds to step 204, in which a control process fordecreasing the opening of the first flow rate control valve 105 isexecuted. Thereby, the refrigeration cycle will be balanced so that thesuperheat temperature T1 increases, and therefore the superheattemperature can be controlled to be closer to the target value.

Thus, by adjusting the opening of the first flow rate control valve 105so as to control the superheat temperature optimally, system performancecan be kept high while avoiding the constraint of constant densityratio.

The foregoing has described an embodiment in which the first flow ratecontrol valve 105 is controlled to optimize the superheat temperature.It is also possible to control the opening of the first flow ratecontrol valve 105 in order to optimize the refrigerant dischargetemperature of the compressor 101, using the outlet temperature sensor112 of the compressor 101 (see FIG. 1). In addition, the bypass circuit106 may include an injector 123 (see FIG. 7) as described in the thirdembodiment.

The foregoing several embodiments have described examples ofrefrigeration cycle apparatus furnished with a fluid machine in which acompressor and an expander are coupled, but it should be understood thatthe present invention is also applicable to separate-type systems inwhich the compressor and the expander are not coupled physically to eachother. In the separate-type system, power consumption of the motor fordriving the compressor can be reduced by converting the mechanical powerthat is recovered by the expander into electric power by a generator,and regenerating the electric power to a power supply line. In such asystem, the frequencies of the compressor and the expander may bechanged individually and freely, so the system is essentially free fromthe constraint of constant density ratio.

However, because the efficiencies of the motor and the generator changedepending of their frequencies, the efficiency of the system may degradesignificantly if the efficiencies of the motor and the generator areignored. For this reason, for the separate-type system as well, it maybe advantageous to provide and utilize the bypass circuit and theinjection circuit as described in the present specification, and thismakes it possible to avoid the constraint of constant density ratiowhile maintaining highly efficient workings of the motor and thegenerator, leading to further enhancement in the system efficiency.

The refrigeration cycle apparatus according to the present invention canbe used for not only hot water heaters and air-conditioners but also forother various electric appliances such as dish dryers and garbagedryers.

1. A refrigeration cycle apparatus comprising: a compressor forcompressing a refrigerant; a radiator for cooling the refrigerantcompressed by said compressor; an expander for expanding the refrigerantcooled by said radiator and recovering mechanical power from therefrigerant under expansion; an evaporator for heating the refrigerantexpanded by said expander and supplying the refrigerant to saidcompressor; a bypass circuit including a flow rate control valve and agas-liquid separator that is provided downstream from said flow ratecontrol valve and that is for separating the refrigerant passed throughsaid flow rate control valve into a gas refrigerant and a liquidrefrigerant, one end of said bypass circuit being connected to an intakeconduit of said expander and the other end of said bypass circuit beingconnected to a discharge conduit of said expander so that a portion ofthe refrigerant passed through said radiator bypasses said expander andis guided to said flow rate control valve and that the liquidrefrigerant separated by said gas-liquid separator returns to saiddischarge conduit of said expander; and an injection circuit, one end ofwhich being connected to a gas outlet portion of said gas-liquidseparator and the other end of which being connected to an intermediatepressure portion of said compressor.
 2. The refrigeration cycleapparatus according to claim 1, wherein said compressor and saidexpander are coupled uniaxially to a motor for driving said compressor.3. The refrigeration cycle apparatus according to claim 1, wherein: saidintermediate pressure portion of said compressor is a portion facing acompression chamber of said compressor; and the gas refrigerant thatflows out of said gas-side discharge portion of said gas-liquidseparator passes through said injection circuit, is injected into saidcompression chamber, and is mixed with the refrigerant undercompression.
 4. The refrigeration cycle apparatus according to claim 1,wherein: said compressor is a multi-stage compressor comprising alow-pressure-side compressor and a high-pressure-side compressor; andsaid intermediate pressure portion of said compressor is a joint portionwhere said low-pressure-side compressor and said high-pressure-sidecompressor are connected.
 5. The refrigeration cycle apparatus accordingto claim 1, wherein said injection circuit comprises a second flow ratecontrol valve.
 6. The refrigeration cycle apparatus according to claim1, wherein said bypass circuit further comprises a throttling deviceprovided downstream from said gas-liquid separator.
 7. The refrigerationcycle apparatus according to claim 1, further comprising: an intaketemperature sensor for detecting a temperature of the refrigerant afterflowing out of said evaporator but before being taken into saidcompressor; and a controller for controlling an opening of said flowrate control valve according to a detection result detected by saidintake temperature sensor.
 8. The refrigeration cycle apparatusaccording to claim 5, further comprising: an outlet temperature sensorfor detecting a temperature of the refrigerant after being dischargedfrom said compressor but before flowing into said radiator; and acontroller for controlling an opening of said second flow rate controlvalve according to a detection result detected by said outlettemperature sensor.
 9. A refrigeration cycle apparatus comprising: acompressor for compressing a refrigerant; a radiator for cooling therefrigerant compressed by said compressor; an expander for expanding therefrigerant cooled by said radiator and recovering mechanical power fromthe refrigerant under expansion; an evaporator for heating therefrigerant expanded by said expander and supplying the refrigerant tosaid compressor; a bypass circuit including a flow rate control valve,one end of said bypass circuit being connected to an intake conduit ofsaid expander and the other end of said bypass circuit being connectedto an intermediate pressure portion of said compressor so that a portionof the refrigerant passed through said radiator bypasses said expanderand is guided to said flow rate control valve; an intake temperaturesensor for detecting the refrigerant after flowing out of saidevaporator but before being taken into said compressor; and a controllerfor controlling an opening of said flow rate control valve according toa detection result detected by said intake temperature sensor.